Airbags are one example of equipment in a vehicle that improves safety when vehicles collide. Some airbags are inflated from the front of a seat, and some airbags are inflated from the side of a seat. With control of the deployment of airbags, deployment speed can be adjusted, and on occasions operation is inhibited, in accordance with judgment as to whether an occupant of a seat is an adult or a child. In order to ensure safety, it is essential to judge accurately whether the occupant of the seat is an adult or a child.
A known occupant-classifying system described in JP2003-276557A includes a sensor for detecting a load imposed on a surface on which an occupant may sit, and, on the basis of the load detected by the sensor, judges whether an occupant of a seat is an adult or a child.
However, the construction of the known occupant-classifying system described in JP2003-276557A does not take into account the movement and change of posture of an occupant while she or he is seated. For example, when an adult occupies a seat and the occupant changes his or her posture, the load imposed on the seat may be reduced as a result of the change in posture, and even when an adult has been occupying a seat, erroneous judgment have been made to the effect that a child is occupying the seat.
In order to overcome the foregoing drawbacks, for example, JP2004-34918 describes an occupant-classifying system which reduces the degree of erroneous judgment of classification of the occupant, by defining threshold load value used for judging change from an adult occupied state to a child occupied state and threshold load value used for judging change from a child occupied state to an adult occupied state different from one another. However, for example, in case of an adult of a light weight occupies a seat and adopts a posture that merely appears to reduce the weight, there is a possibility of erroneous judgment to the effect that a child is occupying the seat. Further, with the construction described in JP2004-34918, once it is judged that the seat is occupied by a child, in case that the threshold load value used for judging change from an adult occupied state to a child occupied state is determined large so that the judgment is unlikely to be switched from a status where a seat is occupied by a child to a status where a seat is occupied by an adult, the erroneous judgment is maintained and there is possibility that judgment cannot be restored.
Further, the construction of the occupant-classifying system described in JP2003-276557 does not take into account the posture change of an occupant while seated, and it is not suggested therein that the degree and frequency of changes of posture of an occupant are influenced by whether or not the occupant is wearing a seatbelt. In general, when an occupant does not wear a seatbelt, the occupant can change posture freely, and the occupant can adopt a posture which largely changes the detectible load, for example, by leaning against a console. Further, because a body of the occupant is free, the occupant probably changes posture frequently. On the other hand, when an occupant wears a seatbelt, a load imposed on the seat is unlikely to fluctuate significantly because the body of an occupant is confined and a change in posture is limited. Further, frequency with which an occupant changes posture is relatively limited. Thus, when a judgment is made using the same threshold load value, irrespective of whether an occupant wears a seatbelt or not, an erroneous judgment is likely to be made because of changes in posture that influence a load when the occupant does not wear the seatbelt. Further, because an occupant changes posture frequently when not wearing a seatbelt, the number of erroneous judgments may be increased, and thus changes of judgment may be increased. On the other hand, when an occupant wears a seatbelt, there is a drawback that a load is unlikely to fluctuate because changes in posture are restricted, and once the erroneous judgment has been made the erroneous judgment becomes implanted.
A need thus exists for an occupant-classifying system which prevents erroneous judgment with accuracy, and facilitates an accurate judge classification of a person occupying a seat.